Due to the combustion of a fuel in internal combustion engines the exhaust gases from combustion contain environmentally polluting substances so that at least partial cleaning of the exhaust gases is required. Particularly in the case of vehicles operated with diesel fuel ever more severe legal requirements in, regard to the composition of the exhaust gases mean that essentially the proportion of nitrogen oxides (NOx) must be considerably reduced in normal operation of the internal combustion engine.
In connection with the operation of diesel internal combustion engines, a method is known in which gaseous ammonia (NH3) is introduced as a reducing agent into the flow of exhaust gases to reduce the content of nitrogen oxides in the exhaust gas, and reacts with the nitrogen oxides in the exhaust gas. In that case the gaseous ammonia reacts with the nitrogen oxides of the exhaust gas selectively to give nitrogen and water.
In the application in the area of internal combustion engines for vehicles an aqueous urea solution is used to prepare ammonia, the urea solution being carried along in the vehicle in its own tank. Accordingly, in addition to the fuel for the internal combustion engine however the aqueous urea solution is stored in a smaller amount and in a separate tank.
In regard to operation of the vehicle in conjunction with exhaust gas cleaning by means of the aqueous urea solution, it is to be noted at winter temperatures considerably below 0° C. that the aqueous urea solution separates out in flakes or freezes at about −11° C. The special tank for the aqueous urea solution therefore requires a heating system so that at low temperatures at least a part of the urea solution in the tank is kept fluid in the short term or is liquefied so that it can be introduced into the exhaust gas flow.
With a suitable arrangement of the separate tank for the fluid reducing agent in the form of the aqueous urea solution, there is the possibility, for suitably taking off the solution from the tank, of causing the fluid to be discharged by way of a pressure head in conjunction with control of a valve. In that connection however it is difficult to ensure an uninterrupted feed in an adequate amount to the exhaust gas installation, in dependence on the operating conditions of the internal combustion engine.
To take off the fluid reducing agent therefore it is possible to use a pump, by means of which the fluid is conveyed from the tank to the exhaust gas installation of the internal combustion engine.
DE 10 2007 050 272 A1 discloses a tank for the storage of a fluid reducing agent, wherein the reducing agent in the form of an aqueous urea solution is heated by means of a heating device at predetermined locations in the tank in which there is provided an additional internal container. The urea solution is taken off by means of a suitable suction line and in conjunction with an associated return line which both dip into the reducing agent disposed in a sump. Thermal coupling of the return line to the heating device is provided for positively influencing thawing of the aqueous urea solution which has frozen under corresponding ambient conditions, at low temperatures. The suction line leads to a conveyor module above the tank, the conveyor module having a pump for conveying the reducing agent from the sump. The conveyor module on the top side of the tank closes off the tank. A filter is arranged at the mouth opening of the suction line in the sump.
In addition DE 10 2006 027 478 A1 discloses a vehicle tank for a fluid reducing agent (for example an aqueous urea solution), wherein the tank has a plurality of chambers and provided in one of the chambers in the form of an internal container is an integrated electric heating means in conjunction with a suction line for taking off the fluid reducing agent. The fluid reducing agent is sucked off by a conveyor module arranged above the tank. In particular a pump is provided in the conveyor module and this arrangement ensures, in conjunction with a further conduit from the fluid reducing agent to the pump, that the pump cannot run dry in normal operation and with a low filling level for the reducing agent.
Such arrangements of tank devices for storing for example a fluid reducing agent with a heating device and a pump device require considerable structural complication and expenditure as a large number of individual parts have to be assembled. The various components of the overall arrangement within and outside the tank (in particular above the tank) result in an enlarged structural volume so that it is not possible to achieve a compact structure in conjunction with easier and thus inexpensive manufacture as in particular the assembly complication and expenditure is considerable and has to be adapted to the factors involved in a particular use.